Interface Control Layer Research Articles

Control of GaAs and InGaAs Insulator-Semiconductor and Metal-Semiconductor Interfaces by Ultrathin Molecular Beam Epitaxy Si Layers

Removal or control of Fermi level pinning is attempted using an ultrathin molecular beam epitaxy (MBE) Si interface control layer (Si ICL) for insulator-semiconductor (I-S) and metal-semiconductor (M-S) interfaces of GaAs and InGaAs. For successful removal of Fermi level pinning at the I-S interface, the Si ICL should maintain an ordered pseudomorphic structure. The optimum thickness of the Si ICL is about 10 Å. Formation of such a Si ICL alone does not remove pinning; subsequent deposition of a SiO2 film is necessary for unpinning. Pinning at the air-exposed surfaces can be removed by combining an HF surface treatment with the Si ICL technique. The Si ICL technique is promising for controlling barrier heights at M-S interfaces.

In Situ Surface State Spectroscopy by Photoluminescence and Surface Current Transport for Compound Semiconductors

By a rigorous computer analysis of the surface recombination process, it is shown that the surface state distributions on semiconductor free surfaces can be determined from a measurement of the dependence of band-edge photoluminescence intensity on the excitation intensity. The measurement of the Fermi level pinning position in the dark by the surface current transport measurement avoids the possible ambiguity of the interpretation. The new technique is successfully applied to variously treated GaAs surfaces and to passivated InGaAs surfaces with and without the ultrathin Si interface control layer.

Characterization of InGaAs surface passivation structure having an ultrathin Si interface control layer

A recently proposed passivation structure of In0.53Ga0.47As surface is characterized by x-ray photoelectron spectroscopy (XPS), capacitance–voltage, and deep-level transient spectroscopy measurements. It uses an ultrathin molecular beam epitaxy Si interface control layer (ICL) and a photochemical vapor deposition (CVD) SiO2 outer insulator. XPS study indicates that growth of Si ICL is coherent and two-dimensional up to about 10 Å beyond which clustering is initiated, and that it is effective in preventing the InGaAs layer from selective oxidation of Ga during photo-CVD SiO2 deposition. C–V and deep level transient spectroscopy (DLTS) measurements give Nss distributions of very different shapes, the latter exhibiting two distinct peaks, which may be erroneously interpreted as defect levels. Suppression of selective oxidation of InGaAs does not alter the shapes of these distributions, although it reduces the magnitude. The results are explained by the disorder-induced gap state model rather than the defect model or the effective work function model.

In0.53Ga0.47As MISFETs Having an Ultrathin MBE Si Interface Control Layer and Photo-CVD SiO2 Insulator

A novel In0.53Ga0.47As MIS structure having an ultrathin MBE Si interface control layer (ICL) between InGaAs and photo-CVD SiO2, is described and applied to fabrication of MISFETs. XPS and electrical characterization show that Si ICL prevents selective oxidation of InGaAs and reduces the interface state density. Depletion mode MISFETs gave an effective channel mobility of 1700 cm2/V·s and excellent stability with drain current drift below 1% up to 104 s.

Control of compound semiconductor–insulator interfaces by an ultrathin molecular-beam epitaxy Si layer

Based on the disorder induced gap state (DIGS) model, an attempt is made to control the insulator–semiconductor (I–S) interfaces of GaAs and In0.53Ga0.47As by an ultrathin surface-oxidized silicon (Si) interface control layer (ICL). A Si ICL is grown on GaAs or InGaAs by molecular beam epitaxy (MBE), and is partially oxidized. Then, a thick SiO2 or Si3N4 layer is deposited by in situ photo-CVD processes. An in situ XPS analysis confirms formation of the intended structures. In the GaAs structure, the state density in the midgap region is remarkably reduced. However, the interface Fermi level is blocked by a high density of interface states near the conduction band minimum, contrary to the recent reports of ‘‘complete unpinning.’’ These states are Si-derived intrinsic states, judging from the band line-up. On the other hand, no such states exist in the InGaAs structure and completely ‘‘unpinned’’ behavior with a very small hysteresis is realized after annealing. The result is interpreted in terms of successful pseudomorphic matching of Si ICL to InGaAs combined with excellent I–S matching between Si ICL and SiO2.